Seatbelt buckle long shot

Guys,
The rear left seatbelt buckle won’t latch when the seatbelt is inserted. Checking the car I found hundreds of little plastic beads under the seat and I believe when these were spilt one or more may have gone inside the buckle.
Can you get access to the buckle internals? I note 2 security torx screws on the cover.
Also any info on replacing if not serviceable? This one is a pain as the buckle mount is also the anchor for the centre strap.
2012 Evoque SD4.

Thanks[/php]

Evan